This was a result, Ferguson reportedly told an investment conference, of Keynes' own lack of children and homosexuality.

Ferguson issued a swift — and seemingly sincere — apology, but it may already be too late. Critics of the noted historian are now going over his history to find more evidence that he truly believes in what he has now admitted to be "stupid and tactless" comments.

Business Insider reached out to Kitson, who offered more detail (emphasis ours):

I was at history seminar given by Niall Ferguson over 20 years ago. I am not good at dates but I think it was around 1990/91. I am better at locations - it was held in the Rushmore Room at St Catharine's College, Cambridge. Ferguson gave a paper, my recollection is that it was on German hyperinflation in the 1920s. But I remember distinctly his response to a question about Keynes: he stated that Keynes and his economics was completely short-termist and that he (Keynes) did not care about the long term or future generations because he was homosexual and did not have children. He elaborated at length on this point - it did not seem as off the cuff remark but a deeply held conviction. I remember being stunned at the time: because of the bigotry and because it showed a complete lack of understanding of Keynes's work. So, it was with a sense of déjà vu that I read the comments that Ferguson has made recently about Keynes.

(Business Insider has asked Ferguson for comment on Kitson's allegation. At the time of writing he has not responded.)

Other critics of Ferguson have been combing through his written work. Justin Wolfers of the University of Michigan tweeted a link to one of Ferguson's books — "The Pity of War", published in 2000 — that seems to link Keynes' sexuality with his economic thought (emphasis ours):

Though his work at the Treasury gratified his self-importance, the war itself made Keynes deeply unhappy. Even his sex life went into a decline, perhaps because the boys he liked to pick up in London all joined up. In September 1915, just eight months after predicitng that German finance was 'crumbling', Keynes was warning that unless peace was achieved by the following April, there would be a catastrophe, as 'the expenditure of the succeeding would rapidly render our difficulties insupportable'.

Another reference to Keynes' sexuality in "The Pity of War" caught the eye of the Economistadentata blog (emphasis ours):

There is, however, no question that a series of meetings with one of the German representatives at Versailles added an emotional dimension to Keynes’ position. Carl Melchior was Max Warburg’s right-hand man (……..) It may be that Keynes’ subsequent declaration that he ‘got to love’ Melchior during the armistice negotiations at Trier and Spa obliquely alluded to a sexual attraction. As we have seen, Keynes was an active homosexual at this time. However, it seems more likely that Keynes was simply captivated by the sound of his own pessimism…..